Useful applications of voidstone

You could also use one as a healing device for undead. Or perhaps a kind of super phylactory for liches perhaps. A wizard could summon one in battle to hurl at an opponent. Or perhaps a wiley assasin could place one inside someones house and the eminations from it would cause emotional or physical decay over time.

That is correct.

Quote from the same source as above:

Anything coming into contact with voidstone is "instantly destroyed" (Fortitude save DC 25). Though it is described as negative energy that has folded in on itself, the effects of voidstone don't appear to be negative energy based.

For comparison, here is part of the description for the sphere of annihilation from the 3.5 SRD:

-420

You want super-weapons, we give super-weapons. Imagine what would Doomguard cook up in Urban planescape setting: "Forget about fireball bombs, and buy our Voidstone bomb with enough firepover that could obliterate entire world or wipe out entire sections of planes."
In hands of Ilithids they could destroy suns with snap of fingers.
In fact Doomguard would not need bombs, they would yust have to figure how to drop one of trough gate that leads to prime.

Here is some other uses for voidstone (if way for keeping it safe is found-wall of force "boxes" spring into mind): As a power component for necromantic spells (or epic spells), and components for rods of desintegration (a little piece would do).

As for weapons: I know that swords are cool (spear would be cool either) and all that, but it would be simpler to make hammer or stone axe or morningstar (wich would basicly be lumps of voidstone on a stick), and since appearently the quantity of woidstone is unimportant for desintegration effect you could just have wand with tiny bit of woidstone on top. After that you just touch people and watch them go poof.

Hmmm. I think force effects can be destroyed by a disintegrate spell, and Voidstone essentially functions as a continual effect Disintegration. A cleric capable of casting 8th level spells could use Greater Spell Immunity against the spell and would be capable of carrying one around for 10 minutes/level, but that's the only way I can think of moving one around safely. And by safely, I mean safe for the owner, not for anyone else

As for the voidstone golem, I love the idea, but it would have to be continually moving or else it would just sink either forever or to the center of gravity if it was on a prime that worked that way. That's an interesting thought, actually. The doomguard hire the PCs to retireve it, and they wind up having to journey to the very center of some backwater prime to recover the blasted thing

With my ideas of a steampunk Planescape, it would be the challenge for a mad scientist/wizard to make a voidstone bullet. It would be in a specially made gun, containing only one bullet. Perhaps an ornate rifle that falls apart after the voidstone bullet is fired, or a very very special dueling pistol.

Though voidstone sort of reminds me of a sphere of annihilation, and the best way around it would be simply to find a Talisman of the Sphere if you want to handle voidstone.

I agree on the sword idea, with a twist.

You know those rare and highly powerful swords that are designed to kill Race X, without hope of resurrection/reincarnation? Demon-slaying swords for example.

A (minute) amount of voidstone may well be one of the many required reagants. (Others are obviously needed as well -- items antithetical to tanar'ri, for example, in that specific case.) The voidstone might well be required for the "kill it, it stays dead" aspect of the enchantment.

I'd say the real challenge would be stopping the damn voidbullet after it had been fired - it just passes through everything at out the other side!

That would be a fun adventure: stopping a void bullet as it flew around Sigil, occasionally bouncing off a creature's spell resistence or The Lady's wards.

Fun for the DM, I mean

Rare? Don't you mean, "Dear Gods, I hope nobody's found a way to search the infinite Negative Energy Plane efficiently -- crap, Mellifleur might have"?

For some reason I can only quote from my own posts now...

Anyway, on the topic of the voidstone bullet in Sigil. Wouldn't it still be affected by gravity? If so, it seems to me that the bullet would follow the natural curve of Sigil's ground.

It would get caught into a permanent loop if it was shot exactly lengthwise or cross wise. Else it would be caught in a more complicated spiral depending on the angle.

And, would this bullet be able to pass through open portals? If so it could just disappear one day only to return days, weeks or months later through a different portal.

-420

Hmm, I think Speeding Bullet, a brief adventure for third level characters, would be a good way for a tabletop group to spend an afternoon. So, who want's to do the honors?